GM Performance 4L60 (not E) behind a ZZ502. Transmission purchased new in 1995. Recently converted from TPI to Holley Carb. Have the PN20-121 kick down bracket for 700R4. The transmission has about 85,000 miles on it.

Whether related to this change or not, began having some issues with the transmission. At first, starting off, it would wind way up before shifting from 1-2. And then, typically only when I let off the gas. Since I had just installed the carb, I assumed a TV cable adjustment. The TV cable was pulled tight at WOT on the carb. I would loosen the cable to lower the shift. Car would be a bit better. Once fully warmed up, would be "ok". Next day, cold same thing. Since it didn't do this before the TPI swap, I assumed it was potentially a bad TV cable of valve. Swapped the cable (Lokar) and new valve. Old one was a 94 and got a new 94 to install. No change.

Thought it might be a viscosity issue. Pumped out the regular fluid and put in synthetic. Actually, could be worse with synthetic. Yesterday's drive was the worse yet. Cable pulled tight at WOT. 1-2 late and 2-3 late. Loosed the cable about 1/16 inch. Now 1-2 was OK and 2-3 was ok. 1-2 at about 15 mph (light to medium throttle). 2-3 was maybe 22-25 mph.

Now, fourth came in at about 30 mph. I know this as I have a idiot light on the 4th gear pressure switch. The switch goes to ground when it has pressure (i.e 4th gear). I also have an idiot light on the TCC lockup.

The bad news. When in fourth, you could press on the accelerator and the only thing that would change is the noise level. I got lot's of HP, but the sense was that the transmission was slipping in 4th badly.

I called some Transmission builders (while I could catch them on Friday). They gave me some potential things to check. Both said it could be the 4th gear band pack went south.

1. Behind the TV valve that I replace is apparently another valve that actually does the work. If that was stuck it could cause the issue. One builder suggested I check that. The other builder stated that when that valve goes, it typically locks into high pressure not low.
2. Check the 4th gear pressure switch. If it was leaking, it would cause low 4th gear pressure. Since the light was coming on, the switch was working, but I pulled it out this morning and put some compressed are on it and it switched and held.
3. The residual fluid in the pan when I dropped it was crystal clean.

Cost of a new one from the builders is pushing $4k, especially the big builders are not down the block, so I have two way freight (core). I have a local builder with a ton of hot rod experience and really good reviews. I could pull it and have it rebuilt with HD stuff for half.

This car is a 38 chevy coupe. With the BBC, virtually everything is shoehorned in. It's would appear that I laid the engine and transmission on stands and assembled the car around them. Pulling the transmission by myself is going to be a big chore. Before I do that, I would really like to see what others might think is my problem. Candidly, it's probably time for rebuild/replacement but really work.

Don
Williamsburg, VA

 

Throttle lever geometry correct???

 

Carb is Holley 870 CFM street avenger. The TV adapter is the Holley P/N 20-121 supposed to be 700R4 to Holley. I compared the Pull length to the TPI that I took off (before putting on the carb) and the pull length is identical to the TPI.

Don

 

The Throttle-Valve cable attaches to linkage at both ends of the Cable.

At the Transmission end of the Cable, the Linkage moves an Arm/ Lever/ Rocker.
This Arm/ Lever/ Rocker pushed against what is called the Throttle-Valve "Plunger and Sleeve" Assembly.
You have a #94 Throttle-Valve "Component Set, and it is good that you replaced it with another #94 Component Set.
These are not interchangeable (Meaning #94 Component Set with Non-#94Component Sets).

The Plunger and Sleeve Assembly control/ dictate Down-Shift Timing and Feel.

The "Other" Valve-Train that you spoke of that is further back in the same Bore (of the Valve-Body) is the "Actual" Throttle-Valve.
This is where the TV (Throttle-Valve) Fluid Pressure is coming from.


Too Tight Cable or Too much Pressure = Late Firm Shifts.
Too Loose Cable or Too Little Pressure = Early Soft Shifts.


Good luck and have fun.

 

It comes into 4th gear early. When in 4th, I can step on the gas and watch the RPM go up, but the car does not accelerate (ever so slightly). RPM will rise 500-600 rpm with no change in vehicle speed.

Don

 

I'm no trans expert. But it seems that one has made it over 25 years and 85k behind a big block. I know some models allow testing 4th pressure, i think... You can probably test 4th pressure on a road test?
As you probably already know incorrect TV can burn one up pretty quick.
If I were you, I would pull it and get it rebuilt if your keeping that car for more years.